Arrangement for relieving electrical switching contacts of current



y 1958 K. M. HARDER 2,842,717

ARRANGEMENT FOR RELIEVING ELECTRICAL SWITCHING CONTACTS OF CURRENT Filed Dec. 28, 1955 INVENTOR. KHIYL NHX HHR'DEK United States Patent F ARRANGEMENT FOR RELIEVING ELECTRICAL SWITCHING CONTACTS OF CURRENT Karl Max Harder, Vaduz, Liechtenstein, assiguor to Patentund Versuchs-Anstalt, Vaduz, Liechtenstein, a company of the Principality of Liechtenstein .Application'Dccember 28, 1955, Serial No. 555,993

Claims priority, application Switzerland December 31, 1-954 .12 Claims. (Cl. 317-511) The present invention relates to electrical switching contacts, more particularly of a type'in whichiextremely exacting demands are made of sensitivecontactmembers in respect of time or in percent and accurate contact 'making without any mechanical changes.

In suchswitching contacts a certain creep of material 'as a result of the electrical processes is inevitable when thecontactsareclosing and opened, evenif'saidcontacts are'most carefully designed and their materials suitably chosen. This creep is assisted, in particular, by the sparking-which occurs when the. contact is opened and by the local heating of points on the surface of the contact. Consequently, the circuit'to be'actuated when sensitive contact members are used is not connected directly, but viaian auxiliary relay with a make'contact. Thedefect of such an arrangement is that the sensitive contact member to be protected'hasto connect the energizing current of the auxiliary relay. Particularly when thecontact member is opened, this current may destroy a the sensitive surface of the contact.

'With this arrangement the-protection of the sensitive 'contact'member is dependent on the operating time of the auxiliary relay. For the contact member to be protectedcnly becomes currentless when the relay has reached'its final switching position. From the moment the relay is energized, that is to say, from the moment the contact member to be protected isclosed, until the "complete closing of the relay contact a certain time elapses, during which the contact member" is not protected. If this time, as is the case with the mechanical relay, is relatively long, it is possible during thistimeforthe flow of current to produce a local heating on theb'ontact surfaces,which may-cause the destruction of'the contact surface. In particular, however, a destruction can be caused during this time by the jarring of the contacts, which can never be completely avoided. In order to remedy this defect, therefore, the operating time of the .auxiliary relay must be made very short. .This, however, cannot be achieved with mechanical means, and so-called electronic means, for instance a-thyratron tube, atransistor :zor apremagnetizedchoke coil, mwstbe-used for .the'purpose. iParticularly if a thyratromtube is used, the operatiingitime can -.-be reducedto such an .extentzthat a destruction of the contact surfacesv :for the abovementioned reasons 'is utterly= impossible. Only one: circuit, t however, can be connected to such switching members. "Thus, if

such means were used, it would not simply -be possible I, 2,842,717. Patented July 8, 1958 ICC both to cut in the consuming device and to bridge the contact to be protected.

It is accordingly an object of the present invention to provide means affording protection during operation of electrical switching contact members.

It is a further object of the invention to provide means eliminating sparking and thus wear of switching contact members during opening movement thereof.

'Still another object of the invention is to provide control means for an electrical circuit, which control means operate electronically and rapidly so as to avoid wear on switching contact means included in said control Yet another object of the invention is to provide control means of the character described, wherein single switching contact means can be included in a-plurality of parallel circuits.

A further object is to provide a control circuit wherein the switching contact member is rendered currentless at the time thatit is opened, sparking and heating of the member :thus being avoided.

Still another object of the invention is to provide means conducive to indicating several conditions in dependence uponclosing of an electrical circuit, the control means for an indicator device including a protected electrical switching contact member controlling a plurality of parallel circuits.

These and other objects and advantages are realized in accordance with the present invention wherein there 'is provided an arrangement for relieving electrical switching contacts of current, more'particularly sensitive contact members which are operated as make contacts, a main switching member, locatedinthe consuming device circuit to-be cut in, being controlled by the make contact to be relieved. The invention is characterized by a bridge circuit consisting of two branches in parallel and supplied at the -latters junction points, .the first branch of which circuit consists of a series connection of two impedances, while the second branch consists of a series connection of parts, of which one part possesses at' least the energizing member causing the main switching member provided with'a self-holding device to be actuated, while the other part possesses at least a make contact operated by the main switching member and connected in series. which extends from the connection point of the imped- The bridge has, furthermore, a diagonal branch ances to the connection point of the aforesaid parts and contains at least the makecontact to be relieved, all the bridge branches being equalized in such a way that after the main switching member-has responded, the diagonal branch is currentless.

A few embodiments of the invention, given by way of example, will now be described in detail with reference to l to -4, Figs. 1 and 2-each reproducing a bridge circuit according to the invention, while Figs. 3 and *4 each illustrates an application of the arrangement according to. the invention in the case of a tolerance measuring instrument.

The bridge circuit shown in .Fig. 1 .consists, by .way of example, of the variableresistance 1 and the fixed resistance 2 which act as impedances U and V, respec- In'the second bridge formed by a gas-filled discharge tube, for instance a thyratron tube 3, in the anode circuit of which the consuming device4 is'located and the cathode resistance 5 of which forms the part Yof the bridge branch. The cathode of'the thyratrontube 3 is connected tothecontrol grid viaa very highzresistance :6. At the branching point of the :two bridge arms'the .sameis. supplied with ,direct voltage, the positive pole of .the current source being 3 a at the terminal 7 and the negative pole at the terminal 8. The make contact 9 of the sensitive contact member is in the diagonal branch of the bridge and, on closing, links the control grid of the thyratron tube 3 to the connection of the two resistances 1 and 2.

Let us suppose that in the state of rest, i. e. when the switch 9 is open, the thyratron tube 3 is currentless. At the make contact 9 there is, in respect of the terminal 8, a positive voltage, viz. a fraction of the bridge supply voltage between the terminals 7 and 8 corresponding to the voltage drop at the resistance 2, which fraction is dependent on the ratio of the resistance values 1 and 2 respectively. If the make contact 9 is closed, this partial voltage, which is positive in respect of the terminal 8, also occurs at the series connection of the resistances 6 and so that the control grid of the thyratron tube 3 becomes positive in respect of the cathode and the tube ignites if the intensity of the grid voltage is adequate. Thus the working current flows in the main circuit from the terminal 7 to the terminal 8 via the consuming device 4, the tube 3 and the cathode resistance 5. The voltage drop produced at the cathode resistance 5 makes the cathode of the thyratron tube 3 positive in respect of the terminal 8. If the resistance values of the bridge circuit are suitably chosen and the variable resistance 1 is appropriately set, it is possible to make the voltage drop at the cathode resistance 5 equal to that at the resistance 2 so that the diagonal branch becomes currentless with the closed make contact 9. By setting the variable resistance 1 in a suitable manner, it is also possible to compensate completely the grid current flowing through the diagonal branch, without the operating state of the thyratron tube 3 being changed since, as is well known, the control grid can no longer influence a current-carrying thyratron tube.

As the diagonal branch becomes currentless immediately after the thyratron tube 3 ignites, the sensitive switching contact 9 is now completely relieved of current and can be opened without any formation of sparks at all and without having any reactive effect on the bridge circuit and the thyratron tube 3. The current is relieved within a very short time after the first operation of the make contact 9, within about 10 micro-seconds and less if the thyratron tubes and resistance values are suitable.

Such a bridge circuit can, of course, as Fig. 2 shows, also be constructed with an auxiliary relay, the make contact 12 of which, connected in series with the consuming device 4, forms the part X of the second bridge branch, while the part Y consists of the exciting winding 10 and a series resistance 11. By suitably balancing all the resistance values itis possible here, too, to cause the relay winding 10 to be energized and the make contact 12 to be closed when the make contact 9 is operated, the voltage produced at the winding 143 and the resistance 11 corresponding, in intensity and polarity, to the voltage drop at the resistance 2, so that the diagonal branch becomes currentless.

Such switching contacts, in which particularly exacting requirements are made in respect of accurate and constant contact making, are usual in, by way of example, tolerance measuring instruments with electrical gauging head. Fig. 3 shows diagrammatically the application of two bridge circuits, similar to that shown in Fig. l, in the case of such a gauging head, the feeler 13 of which scans the specimen 16 and tests its theoretical size, closing the contact 14 when the upper tolerance limit is reached and the contact 15 when the lower tolerance limit is reached.

The contact 14 controls the thyratron tube 17 with the cathode resistance 18, the grid resistance 19 and the consuming device designed as a pilot lamp 20, which parts form the XY branch of a bridge circuit, the UV branch of which is formed by the resistances 21 and 22.

The contact 15, on the other hand, controls the thyratron tube 23with the cathode resistance 24, the grid resistance 4 25 and the consuming device designed as a pilot lamp 26, which parts form the XY branch of a second bridge circuit, the UV branch of which is represented jointly with that of the first bridge circuit by the resistances 21 and 22. The two bridge circuits are supplied from an alternating-current source 28 via the transformer 27.

The cathode resistances 18 and 24 respectively are here designed to be variable in order, after contact has been made between the feeler 13 and the contacts 14 and 15 respectively and the thyratron tubes 17 and 23, respectively, have been ignited, to equate the voltage drop at the cathode resistances 18 and 24 respectively to that at the resistance 22 and thus to make the relevant contact 14 or 15, respectively, currentless. In such an application it is necessary that the thyratron tubes 17 or 23 should be extinguished immediately after the feeler 13 leaves the contact 14 or 15, respectively, assigned to them. This is achieved here by supplying the bridge circuits with alternating voltage, each thyratron tube, ignited by a contact made by the feeler 13, carrying current only in the positive half-period of the supply voltage, but being extinguished in the negative half-period. Thus, when the feeler 13 is raised from one of the two contacts 14 or 15, the thyratron tube 17 or 23 respectively assigned thereto will become currentless at the next negative halfperiod of the supply voltage and, owing to the absence of the positive grid voltage, cannot ignite again even during the positive half-periods of the supply voltage.

In the case of a circuit according to Fig. 3, which is supplied with alternating voltage, however, the diagonal branch connected on each occasion is currentless for only part of the supply voltage period, namely, when the appurtenant thyratron tube is current-carrying, while in the negative half-period of the supply voltage an opposed current flows through the diagonal branch. In order to avoid this disadvantage of a circuit according to Fig. 3 in the case of alternating-current operation, a rectifier is suitably inserted in the supply line to each of the contacts 14 and 15, which rectifier prevents a flow of current from the cathode resistance 18 or 24 respectively to the feeler 13.

A further embodiment with a differently designed gauging head and suitable for operation from a directcurrent source is shown in Fig. 4. In this case, the specimen 31 is tested in respect of its theoretical size by the feeler 30. The spring 34 presses the feeler 30 downwardly. If, therefore, there is no specimen under the feeler, the latter presses down the contact lever 35 via the spherical cap 37 and said lever, in its turn, presses down the lever 36 via the spherical cap 38 until the lever 36 touches the stop 32, whereby the rest position of the gauging head is reached. The adjustable cooperating contacts 39 and 40 are both open in this position. The two contact levers 35 and 36 are grounded.

If too small a specimen 31 is placed beneath the feeler 30, the latter will indeed be raised, but not to such an extent that the lever 36, which follows it owing to the spring 41, touches its cooperating contact 40. Thus, both contacts 39 and 40 remain open. A specimen of the correct size, on the other hand, raises the feeler to such an extent that the lever 36 touches the contact 40, while the lever 35 is not yet touching the contact 39 (position illustrated). If, on the other hand, the specimen 31 is too large, the feeler will be raised to such an extent that the lever 35, which follows it owing to the spring 42, touches the contact 39. In this case, therefore, both the contacts 39 and 40 are in electrical contact with the levers 35 and 36 assigned to them.

The contact 39 controls the thyratron tube 43 with the cathode resistance 44, the grid resistance 45 and the consuming device designed as a pilot lamp 46, which parts form here the XY branch of a bridge circuit, the UV branch of which is represented by the resistances 47 and 48. The contact 40, on the other hand, controls the thyratron tube 49 with the cathode resistance 50 and the grid resistance 51, which parts form the XY branch of 'a second bridge circuit, the UVbranchof which is represented 'jointly with that-o'f the'first bridg'ecircuit-by the resistances 47 and 4'8. The pilot lamp 52 is, in this case,

in series connection with the resistance 53 and a rectifier 54 between the cathodes of the tubes 43 and 49. A similar series circuit, consisting of the pilot lamp 55, the resistance 56 and the rectifier 57, is located between the cathode of the tube 49 and the grounded bridge joint 58. Both bridge circuits are here supplied by a direct-current source 59.

As long as the contacts 39 and 40 of the gauging head are open, the two thyratron tubes are currentless. In this state, a current flows from the branching point 58 through the pilot lamp 55 and the rectifier 57 via the cathode resistance 50. The pilot lamp 55 lights up and indicates that the feeler device is at the undersize position. In this case, a partial current flows from the cathode of the tube 49 through the lamp 52, the latters series resistance 53 and the cathode resistance 44 of the tube 43. The cathode resistance 50, however, is small in comparison with the bridge resistance 48, or, respectively, it is small in comparison with the internal resistance of 55 and the latters series resistance 56. In this way the voltage drop via the cathode resistance 50 is slight so that only a very small current flows through the pilot lamp 52, which current is not able to make the said lamp light up. As soon, however, as the contact 40 on the gauging head closes, the branching point 58 is connected to the grid of the tube 49 via the rectifier 60. As the potential at the point 58 is positive, in contrast to the potential at the cathode of the tube 49, the tube ignites. As soon as this has happened, an equality of potential prevails between the tubes cathode and point 58. Thus, the flow of current through the pilot lamp 55 ceases and at the same time the tllOW of current through contact 40 via rectifier 60 to the grid of the tube 49 also ceases. Owing to the ignition of the tube 49, however, the voltage drop at the resistance 50 has now become substantially larger. As a result, a flow of current is now produced via the pilot lamp 52 and the cathode resistance 44, which flow is sufiiciently large to cause the lamp 52 to light up brightly. The lamp 52 indicates in this way that the gauging head is at the correct size position.

If now the lever 35 touches the contact 39, the point 58 will thereby be connected to the grid of the tube 43. As the potential at the point 58 is positive in contrast to the potential at the cathode of the tube 43, the latter will ignite. A current now flows through the pilot lamp 46 which is thus caused to light up. An equality of potential now prevails between the cathodes of both tubes so that the flow of current through the lamp 55 ceases and said lamp goes out. The pilot lamp 46 indicates that the gauging head is now at the oversize position.

Owing to the equality of potential between the cathodes of the two tubes 43 and 49 and to the ceasing, connected therewith, of the flow of current through the lamp 52, the potential at the cathode of the tube 49 changes a little, becoming somewhat more positive in comparison with 58. In order that no flow of current through the contact 40 should occur, rectifiers 57 and 60 are provided. The rectifier 61 serves the corresponding purpose in the case of contact 39.

If the feeler now returns to its rest position, so that the contacts 39 and 40 open, the state of the thyratron tubes nevertheless remains unchanged; i. e., as before, that pilot lamp lights up which has signalled the last position of the feeler. Before a new test is performed, therefore, the anode circuit of the tubes must be briefly interrupted so that the pilot lamps, too, can return to the rest position, for which purpose the pressure switch 62 is used.

In the embodiments given by way of example in Figs. 1 to 4 either a thyratron tube or an auxiliary relay has been indicated as the main switching member. The

bridge circuit, however, :can of course also beused with other types of main switching members, for instance with premagnetized iron-cored choke coils, with tube and transistor sweepcircuits, etc.

Various changes and modifications :may be made without departing from the spirit and scope of the present invention and it is intended that such obvious changes and modifications be embraced by the annexed claims.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that What I claim is: 1. An arrangement for relieving electrical switching contacts of current, more particularly sensitive contact members which are operated as make contacts, a main switching member located in the consuming device circuit to be cut in being controlled by the make contact to be relieved, characterized by a bridge circuit consisting of two branches in parallel and supplied at the junctions of said branches, the first branch of which circuit consists of a series connection of a first and a second irn' pedance, while the second branch consists of a series connection of a first and a second circuit element, of which one of said elements possesses at least the energizing member causing the main switching member provided with a self-holding member to be operated, while the other part possesses at least a make contact connected in series and operated by said main switching member, further characterized by a diagonal branch which extends from the connection point of the first and second impedances to the connection point of the first and second element and contains at least the make contact to be relieved, all the bridge branches being so equalized that after the main switching member has responded, the diagonal branch is currentless.

2. An arrangement according to claim 1, characterized by a thyratron tube which is provided with a cathode resistance and a grid resistance. lying directly on the cathode, and forms said first and second element bridge branch, said diagonal branch being directly connected to the control grid of said thyratron tube.

3. An arrangement according to claim 2, characterized by the fact that in the state of rest the thyratron tube is currentless, the grid and cathode resistances being selected such that they form means for producing a voltage at the grid and cathode resistances on the operation of said make contact in said diagonal branch sufficient to ignite said thyratron tube.

4. An arrangement according to claim 3, wherein said first and second impedances include means for producing in the ignited operating state a voltage at the cathode and grid resistances of the same intensity and polarity as the voltage prevailing at the connection point of the impedances of the other bridge branch, so that the diagonal branch is currentless.

5. An arrangement circuit according to claim 2, characterized by the fact that the consuming device is in the anode circuit of the thyratron tube.

6. An arrangement according to claim 2, characterized by the fact that the bridge circuit is connected to an alternating current source.

7. An arrangement according to claim 1, characterized by a relay as main switching member, the exciting winding of which belongs to said second element and a make contact of which in series connection with an impedance forms said first element.

8. An arrangement according to claim 7, wherein the ratio of the resistance of the first and second elements is the same as the ratio of the first and second impedances.

9. An arrangement according to claim 7, wherein the impedance in said first element is formed at least in part by the consuming device.

10. An arrangement according to claim 1, wherein the make contact in said diagonal branch is the tolerancedeterrnining switching contact of a tolerance measuring instrument.

7 8 11. An arrangement according to claim 10, compris- 12. An arrangement-according to claim 11, charactering two bridge circuits each with one make contact in ized.by the fact, that said two bridge circuits have a said diagonal branch, of which one of the switching concommon first and second impedance.

tacts is for the upper limit of the tolerance range "and the other switching contact is for the lower limit of same. 5 No references c ted. 

